GPS (Global Positioning System) has been used extensively for navigation, positioning, and other research applications. It includes a group of satellites transmitting very precise signals. The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth with 12-hour periods. These space vehicles (SV's) send radio signals that consist of time-tagged data bits marking the time of transmission, and information on the locations of the SV's, at the time they are transmitted. GPS receivers convert the received SV signals into the receivers' position. Four satellites are required to compute the four dimensions of X, Y, Z (position) and time. GPS receivers at precisely known reference locations can provide corrections and relative positioning data for receivers at other locations. Another use of GPS is to provide precise time and frequency standards through the use of precise clocks on-board the SV's.
For about two decades, GPS receivers have been used primarily in the outdoor environment. It is more challenging to use them indoors. The signal strengths from the SV's can be much reduced, such as by two orders of magnitude. A number of companies have been developing indoor GPS receivers. They are enticed by the US Federal Communications Commission's E911 telecommunication initiatives, which require wireless phone providers to locate any phone making a 911 emergency call.
The E911 initiative will greatly increase the proliferation of GPS devices. Telematics—the field of mobile services delivered wirelessly to in-vehicle devices—will further help GPS penetrate into different sectors of the society. One of the most visible manifestations of telematics is GPS-based navigation systems. They provide turn-by-turn directions and other information wirelessly to vehicle operators.
The amount and availability of GPS information will dramatically increase in the coming years. One challenge this will present is how to effectively use such information. There are needs for techniques to efficiently and intelligently analyze, process and present GPS information.